Synthesis and characterization of coordination polymers of a carboxylato cyclophane with metal [Zn(II) and Cd(II)]-2,2′-bipyridines

N,N′,N′′,N′′′-Tetrakis(3-carboxy-propionyl)-1,6,20,25-tetraaza-[6.1.6.1] paracyclophane, H₄cp has been complexed with metal (Zn(II) and Cd(II)) 2,2′-bipyridyls. The resulting complexes of the composition [{Zn(2,2′-bpy)}₂(cp)]_n·4H₂O 1 and [{Cd(2,2′-bpy)}₂(cp)]_n·5H₂O 2 (2,2′-bpy = 2,2′-bipyridine) have been characterized using spectroscopic (IR, solid state UV–Vis), elemental analysis and single-crystal X-ray diffraction measurements. In these complexes the cyclophane coordinates in different modes, and in complex 2, Cd(II) is hepta-coordinated. However, under harsh reaction conditions (using excess nitric acid and a longer reaction time) debranching of the cyclophane is observed in the reaction of Zn(2,2′-bpy)(NO₃)₂ with H₄cp, and a complex of the composition [Zn(2,2′-bpy)(Suc)]_n3 (suc = succinate) is isolated. Using non-covalent interactions, complexes 1 and 2 provide 3D supramolecular structures, whereas an infinite 1D chain structure is observed for complex 3. The thermal and photoluminescence properties of the complexes have also been studied.     

Computing Eigen value equation and modal dispersion characteristics of an elliptical Bragg waveguide

Using the method of separation of variables in the elliptical coordinate system, a recursive formula for the electromagnetic fields in a new type of Bragg waveguide having elliptical core cross section with multilayered cladding is derived. The eigen equation is written in the form of Mathieu and the modified Mathieu functions and a dispersion relation is obtained for various modes supported by the proposed Bragg waveguide. The cutoff frequencies for several lower order even-odd modes have been calculated and their propagation characteristics are plotted. The results show that the dispersion curves are discontinuous and modes can exist only in particular wavelength bands. The effects of elliptical eccentricity on the mode cutoff values and mode transmission are addressed. Finally, the modal birefringence in the said waveguide is also estimated.     

Phenacyl bromide: A versatile organic intermediate for the synthesis of heterocyclic compounds

Phenacyl bromides are used as a building blocks in synthetic organic chemistry, which serves as a key model for the development of various biologically important heterocyclic compounds and other industrially important scaffolds. This review covers recent synthetic advances in the preparation of heterocyclic compounds utilizing various phenacyl bromides. A wide range of five- and six-membered heterocyclic compounds as well as fused heterocyclic compounds were synthesized efficiently from the phenacyl bromide precursors through one-pot multicomponent reactions.     

Synthesis of mixed metal oxide nanoparticles of SnO<Subscript>2</Subscript> with SrO via sol–gel technology: their structural,optical, and electrical properties

Mixed metal oxides of tin with strontium (xSnO₂.SrO) in different molar ratio {where x?=?1 (1), 2 (2), 4(3); SnO₂ doped with Sr⁺²(4), SnO₂ doped with Sr⁺² and co-doped with F^?(5)} have been prepared by sol–gel technology in basic medium using SnCl₂.2H₂O as precursor in isopropanol as solvent. Structural analysis by XRD patterns have shown formation of particles at nanoscale and phase separation of SnO₂ in tetragonal rutile framework in these mixed metal oxides. This fact was further supported by TEM. SEM images of all these samples have shown formation of various geometrical patterns ranging from spherical particles to nanorods. In the IR spectra of all these oxides, Sr–O absorption bands were present only in sample (1). UV–Vis spectroscopy has shown reduction in optical band gap in mixed metal oxides and the lowest value of band gap was observed for sample (3). Photoluminescence spectra of all these derivatives are found to be almost similar again indicated retention of tetragonal rutile SnO₂ framework. I–V curves of all these oxides are non-linear and lowest resistance was observed for sample (3). This fact was further supported by impedance measurements.

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Green analytical chemistry-driven response surface modeling to stability-indicating chromatographic method for estimation of cilnidipine and application of high-performance thin-layer chromatography–mass spectrometry for characterization of degradation products

Cilnidipine is a calcium channel blocker that is used to treat cardiac diseases such as angina and high blood pressure. Several column and planar chromatographic methods for estimating cilnidipine in pharmaceutical dosage forms have been documented. However, these method developments have been carried out employing organic solvents such as acetonitrile, methanol, toluene, chloroform, and others as mobile phase components or as sample pretreatment diluents. These organic solvents are neurotoxic and teratogenic to humans and aquatic animals, according to International Council for Harmonization Q3C (R8) recommendations. According to the green analytical chemistry approach, such organic solvents should be reduced or removed during the development of chromatographic methods for environmental protection and the safety of human and aquatic animal life. As a result, the stability-indicating chromatographic estimation of cilnidipine was performed utilizing less toxic organic solvents. To prevent organic solvent waste during method development, mobile-phase optimization was performed using the design of experiment-based response surface modeling. Cilnidipine has been subjected to hydrolysis, oxidation, photolysis, and dry-heat decomposition to determine its stability. The greenness profiles of the suggested and published chromatographic methods were examined using the national environment method index, analytical greenness calculator, green analytical procedure index software, and eco-scale assessment tool.     

Development and validation of a visible absorption densitometry method for quantitation of conessine in Holarrhena antidysenterica (Kurchi)

A selective, precise, and accurate high-performance thin-layer chromatographic (HPTLC) method has been proposed for the analysis of conessine in Holarrhena antidysenterica. The method involves visible densitometric evaluation of conessine resolving it by HPTLC on aluminium-based silica gel plates. For visible densitometric evaluation, peak areas were recorded at 520 nm after the resolved bands were derivatized with Dragendorff's reagent and then sprayed with a 10% solution of aqueous sodium nitrite which resulted in reddish brown color. The correlation between the concentration and area was found to be linear within the range of 10 to 60 ng/spot. The method was validated for precision (interday and intraday), repeatability, and accuracy. Mean recovery for conessine was 98.34-100.25%. The method was applied for the quantitation of conessine in Kurchi. The proposed HPTLC method was found to be precise, specific, sensitive, and accurate and can be used for routine analysis of Kurchi.     

Facile and convenient strategy towards synthesis of 4-substituted 2-aminothiazolo[4,5-d]pyridazinones

Convenient synthesis of 4-substituted 2-aminothiazolo[4,5-d]pyridazinones has been achieved in 12 steps with overall yield of 19% by employing Grignard reaction as the key step. The route utilizes well established thiazole ring formation followed by Grignard reaction to introduce substitution at 4-position effectively. In addition to the use of inexpensive chemicals, the present route first time gave access to the 4-substituted 2-aminothiazolo [4,5-d]pyridazinones with free amino group at C-2 position.     

Synthesis, characterization and chelating properties of poly [azo-(6-hydroxy-1,3-phenylene)]

Poly [azo(6-hydroxy-1,3-phenylene)] (PAHP) was prepared by alcoholic alkaline reduction of 2,4-dinitro phenol (DNP). The polymers prepared at various time intervals were characterized by elemental analyses, IR spectra and thermogravimetric analysis. The number average molecular weight was determined by non-aqueous titration. Viscometric study in DMF of all the three polymers were carried out and indicates polyelectrolyte behaviour. Viscometric study in DMF-water (85:15)(v/v) containing 1%KBr shows normal behaviour. Polymeric metal chelates of Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺, Mn²⁺ and Cr²⁺ with PAHP polymer were prepared and characterized.     

Mesogenic benzothiazole derivatives with methoxy substituents

Two new mesogenic homologous series containing 6-methoxybenzothiazole ring at the terminus of the molecule, viz. 2-(4′-n-alkoxyphenylazo)-6-methoxybenzothiazoles and 2-[4′-(4″-n-alkoxy-benzoyloxy) phenylazo]-6-methoxybenzothiazoles were synthesized. In series I,n-butyloxy to n-tetradecyloxy derivatives exhibit nematic mesophase. Smectic A mesophase commences from then-dodecyl-oxy derivative as a monotropic phase and is retained up to the last member synthesized. All the members of series II exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally related series to evaluate the effect of the benzothiazole ring and the methoxy substituent on mesomorphism. This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore during 9–11 October 2003